In general, a real time clock (referred to as RTC below) has a power supply independent of a main function in a chip, and the RTC is used in a case where a main power supply is stopped to reduce power consumption and in a case where time information continuous to time information before the power supply is stopped is required after the power supply is restored (refer to Patent Document 1).
With progress in downsizing of digital circuits and reduction in power consumption due to miniaturization of a complementary metal oxide semiconductor (CMOS) process in recent years, a proportion of power consumed by a leak current in power consumed by the digital circuits has been increased in the miniaturization process. Therefore, demands to turn off an entire chip including the RTC (referred to as “deep sleep” below) have been increased.